Surfactants for tertiary mineral oil extraction based on branched alcohols

ABSTRACT

Surfactants of the general formula R 1 —X where R 1  is an aliphatic C 17 H 35 -alkyl radical and X is a hydrophilic group, and the mean degree of branching of the R 1  radical is from 2.8 to 3.7. Mixtures which comprise such surfactants and the use of such surfactants and of mixtures thereof for tertiary mineral oil extraction.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/420,248, filed Apr. 8, 2009, which claims the benefit of U.S.Provisional Application No. 61/058,743, filed Jun. 4, 2008, and claimspriority from European Application 08154303.5 filed Apr. 10, 2008, theentire contents of which are incorporated herein by reference.

The invention relates to surfactants of the general formula R¹—X whereR¹ is an aliphatic C₁₇H₃₅-alkyl radical and X is a hydrophilic group,and the mean degree of branching of the R¹ radical is from 2.8 to 3.7.It further relates to mixtures which comprise such surfactants and tothe use of such surfactants or of mixtures thereof for tertiary mineraloil extraction.

In natural mineral oil deposits, mineral oil is present in the cavitiesof porous reservoir rocks which are sealed toward the surface of theearth by impermeable top layers. The cavities may be very fine cavities,capillaries, pores or the like. Fine pore necks may, for example, have adiameter of only approx. 1 μm. As well as mineral oil, includingfractions of natural gas, a deposit comprises water with a greater orlesser salt content. The salt content of deposit water is not rarelyfrom 5 to 20% by weight; but there are also deposits with a salt contentof up to 27% by weight. The dissolved salts may, for example, be alkalimetal salts; in some deposits, the deposit water, however, alsocomprises more than relatively high contents of alkaline earth metalions, for example up to 5% by weight of calcium ions and/or magnesiumions.

In mineral oil extraction, a distinction is drawn between primary,secondary and tertiary extraction.

In primary extraction, the mineral oil flows, after commencement ofdrilling of the deposit, of its own accord through the borehole to thesurface owing to the autogenous pressure of the deposit. The autogenouspressure can be caused, for example, by gases present in the deposit,such as methane, ethane or propane. By means of the primary extraction,according to the deposit type, it is, though, usually possible toextract only approx. 5 to 10% of the amount of mineral oil present inthe deposit; thereafter, the autogenous pressure is no longer sufficientfor extraction.

After primary extraction, secondary extraction is therefore used. Insecondary extraction, in addition to the boreholes which serve for theextraction of the mineral oil, the so-called production bores, furtherboreholes are drilled into the mineral oil-bearing formation. Water isinjected into the deposit through these so-called injection bores inorder to maintain the pressure or to increase it again. As a result ofthe injection of the water, the mineral oil is forced through thecavities in the formation slowly, proceeding from the injection bore, inthe direction of the production bore. However, this only works for aslong as the cavities are completely filled with oil and the more viscoseoil is pushed onward by the water (see FIG. 1). As soon as the mobilewater breaks through cavities, it flows on the path of least resistancefrom this time, i.e. through the channel formed, and no longer pushesthe oil onward. This situation is shown in FIG. 2: owing to thedifferent polarity of oil and water, a high interface energy orinterfacial tension arises between the two components. The two thereforeadopt the smallest contact area, which results in a spherical oildroplet which no longer fits through the fine capillaries. At the end ofthe water flow, the oil is thus trapped in the capillaries indiscontinuous form (isolated spherical droplets).

By means of primary and secondary extraction, generally only approx. 30to 35% of the amount of mineral oil present in the deposit can beextracted.

It is known that the mineral oil yield can be enhanced further bymeasures for tertiary oil extraction. A review of tertiary oilextraction can be found, for example, in the Journal of PetroleumScience and Engineering 19 (1998) 265-280. Tertiary oil extractionincludes thermal methods in which hot water or steam is injected intothe deposit. This lowers the viscosity of the oil. The flow medium usedmay also be gases such as CO₂ or nitrogen.

Tertiary mineral oil extraction also includes methods in which suitablechemicals are used as assistants for oil extraction. These can be usedto influence the situation toward the end of the water flow and as aresult also to extract mineral oil hitherto held firmly within the rockformation.

Viscous and capillary forces act on the mineral oil which is trapped inthe pores of the deposit rock toward the end of the secondaryextraction, the ratio of these two forces relative to one another beingdetermined by the microscopic oil separation. By means of adimensionless parameter, the so-called capillary number, the action ofthese forces is described. It is the ratio of the viscosity forces(velocity×viscosity of the forcing phase) to the capillary forces(interfacial tension between oil and water×wetting of the rock):

$N_{c} = {\frac{\mu\; v}{\sigma cos\theta}.}$

In this formula, μ is the viscosity of the fluid mobilizing mineral oil,ν is the Darcy velocity (flow per unit area), σ is the interfacialtension between liquid mobilizing mineral oil and mineral oil, and θ isthe contact angle between mineral oil and the rock (C. Melrose, C. F.Brandner, J. Canadian Petr. Techn. 58, October-December, 1974). Thehigher the capillary number, the greater the mobilization of the oil andhence also the degree of oil removal.

It is known that the capillarity number toward the end of secondarymineral oil extraction is in the region of about 10⁻⁶ and that it isnecessary to increase the capillarity number to from about 10⁻³ to 10⁻²in order to be able to mobilize additional mineral oil.

To this end, for example, the interfacial tension σ between mineral oiland the aqueous phase can be lowered by the addition of suitablesurfactants. This technique is also known as “surfactant flooding”.Suitable surfactants for surfactant flooding are especially surfactantswhich can lower σ to values of <10⁻² mN/m (ultralow interfacialtension). In this manner, it is possible to change the shape of the oildroplets and to force them through the capillary orifices by means ofthe flooding water.

It is desired that the oil droplets subsequently combine to a continuousoil bank. This is shown schematically in FIG. 3. This has two kinds ofadvantages: firstly, as the continuous oil bank advances through newporous rock, the oil droplets present there can merge with the bank.Moreover, the combination of the oil droplets to form an oil banksignificantly reduces the oil-water interface, and surfactant which isno longer required is thus released. The released surfactant can thenmobilize oil droplets remaining in the formation. This is shownschematically in FIG. 4. An ultralow interfacial tension between thewater phase and the oil phase is also required to combine the oildroplets to an oil bank and to incorporate new oil droplets into the oilbank. Otherwise, individual oil droplets remain or are not incorporatedinto the oil bank. This reduces the efficiency of the surfactantflooding.

In general, after the surfactant flooding, to maintain the pressure,water is not injected into the formation, but rather a higher-viscosityaqueous solution of a polymer with high thickening action. Thistechnique is known as “polymer flooding”.

In surfactant flooding, the surfactants should form a microemulsion(Winsor type III) with the water phase and the oil phase. Amicroemulsion (Winsor type III) is not an emulsion with particularlysmall droplets, but rather a thermodynamically stable, liquid mixture ofwater, oil and surfactants which has a very low interfacial tension andusually possesses a low viscosity. It is in equilibrium with excesswater and excess oil. A low viscosity is desirable to transport theemulsion in the mineral oil formation. At an excessively high viscosityof the phase to be transported, a very high pressure would have to beapplied in the course of polymer flooding. This is firstly expensive,but there is in particular also the risk that the pressure mightundesirably blast new cavities in the mineral oil formation. Inaddition, a combination of the mobilized oil droplets to a continuousoil bank is hindered in the case of excessively high viscosities.

The requirements on surfactants for tertiary mineral oil extractiondiffer significantly from the requirements on surfactants for otherapplications.

The surfactants should reduce the interfacial tension between water andoil (typically approx. 20 mN/m) to particularly low values of less than10⁻² mN/m, in order to enable sufficient mobilization of the mineraloil. This has to be done at the customary deposit temperatures of fromapprox. 30 to approx. 130° C. and in the presence of water with a highsalt content, especially also in the presence of high contents ofcalcium and/or magnesium ions; the surfactants must thus also be solublein deposit water with a high salt content. The temperature window withinwhich a microemulsion forms should at the same time be very wide. Toprevent surfactant losses in the formation, the surfactants should havea low tendency to form viscous or large surfactant superstructures, andhave a low adsorption capacity. Moreover, the surfactants should have ahigh chemical stability under the conditions existing in the formation.This includes in particular a high long-term stability: the migrationvelocity of the surfactant flood in the formation is often less than 1m/day. According to the distance between injection bore and extractionbore, the residence times of the surfactant in the mineral oil depositmay be several months.

For use in the tertiary mineral oil extraction, various surfactants andmixtures of surfactants have already been proposed.

U.S. Pat. No. 3,811,505 discloses a mixture of an anionic surfactant anda nonionic surfactant for use in deposits whose deposit water comprisesfrom 0.5 to 0.9% by weight of polyvalent ions. The anionic surfactantsare alkyl sulfonates or alkyl phosphates having in each case from 5 to25 carbon atoms, alkylaryl sulfonates or alkylaryl sulfonates whosealkyl radical has in each case from 5 to 25 carbon atoms. The nonionicsurfactants are polyethoxylated alkylphenols which have from 6 to 20ethoxy groups and whose alkyl radical has from 5 to 20 carbon atoms, orpolyethoxylated aliphatic alcohols having from 6 to 20 carbon atoms andfrom 6 to 20 ethoxy groups.

U.S. Pat. No. 3,811,504 discloses a mixture of 2 different anionicsurfactants and a nonionic surfactant for use in deposits whose depositwater comprises from 0.15 to 1.2% calcium and magnesium ions. The formeranionic surfactant comprises alkyl or alkylaryl sulfonates, the secondcomprises alkyl polyethoxy sulfates, and the nonionic surfactantcomprises polyethoxylated aliphatic or aromatic alcohols. Surfactantmixtures of similar composition are disclosed, for example, by U.S. Pat.No. 3,508,621, U.S. Pat. No. 3,811,507 or 3,890,239.

U.S. Pat. No. 4,077,471 discloses a surfactant mixture for use in aformation whose deposit water has a salt content of from 7 to 22%. Themixture comprises a water-soluble alkylpolyalkoxyalkyl sulfonate oralkylarylpolyalkoxyalkyl sulfonate, and a water-insoluble nonionicsurfactant composed of an ethoxylated aliphatic alcohol or anethoxylated alkyl-substituted aromatic alcohol.

EP 003 183 B1 discloses surfactants of the general formulaR—O-polypropoxy-polyethoxy-X, where X is a sulfate, sulfonate, phosphateor carboxylic acid group. In a preferred embodiment of the invention, Rmay be a branched alkyl radical having from 10 to 16 carbon atoms, forexample an isotridecyl radical.

U.S. Pat. No. 3,675,716 discloses a mixture of an anionic surfactant anda branched alkoxylated alcohol sulfate where the branching site is notmore than one carbon atom away from the carbon atom to which the sulfategroup is attached.

U.S. Pat. No. 5,849,960 discloses branched alcohols having from 8 to 36carbon atoms. The degree of branching is at least 0.7 and preferablyfrom 1.5 to 2.3, less than 0.5% quaternary carbon atoms being present,and the branches comprising methyl and ethyl groups. Also described isthe further processing of the alcohols to corresponding surfactants,specifically alkoxylates, sulfates or alkoxysulfates, and the usethereof for producing biodegradable washing compositions.

EP 958 267 B1 discloses branched alcohols having from 11 to 36 carbonatoms. The degree of branching is from at least 0.7 to 3.0, preferablyfrom 1.5 to 2.3, less than 0.5% quaternary carbon atoms being present,and the branches comprising methyl and ethyl groups. Also described isthe further processing of the alcohols to corresponding surfactants,specifically alkoxylates, sulfates or alkoxysulfates, and the usethereof for producing biodegradable washing compositions.

U.S. Pat. No. 6,222,077 discloses a process for preparing surfactants,in which linear C₆ to C₁₀ olefins are dimerized to C₁₂ to C₂₀ olefins,the resulting olefins are converted to C₁₃ to C₂₁ alcohols and thealcohols are converted to corresponding branched surfactants. The meandegree of branching of the alcohols is from 0.9 to 2.0, less than 25% ofthe branches being arranged in the C₂ or C₃ position to the OH group.

US 2006/0184986 discloses the use of a mixture of at least one branchedaliphatic anionic surfactant and an aliphatic nonionic surfactant formineral oil extraction. The branched aliphatic radical has preferablyfrom 10 to 24 carbon atoms and the degree of branching is from 0.7 to2.5.

US 2006/018486 discloses the use of a mixture of at least one branchedaliphatic anionic surfactant and an aliphatic nonionic surfactant formineral oil extraction. The branched aliphatic radical has preferablyfrom 10 to 24 carbon atoms and the degree of branching is from 0.7 to2.5.

It was an object of the invention to provide improved surfactants fortertiary mineral oil extraction.

Accordingly, surfactants of the general formula R¹—X have been found,where R¹ is an aliphatic C₁₇H₃₅-alkyl radical and X is a hydrophilicgroup, and the mean degree of branching of the R¹ radical is from 2.8 to3.7, preferably from 2.9 to 3.6.

In a preferred embodiment of the invention, X is a group selected fromthe group of sulfonate groups, polyoxyalkylene groups, anionicallymodified polyoxyalkylene groups, glucoside groups or amine oxide groups.

A further preferred embodiment of the invention concerns surfactantmixtures of at least two different surfactants, at least one of whichbeing a surfactant R¹—X.

Additionally found has been the use of surfactants R¹—X or mixturesthereof for tertiary mineral oil extraction.

APPENDED DRAWINGS

FIG. 1 Situation at the start of secondary oil extraction: completelyoil-filled rock pore.

FIG. 2 Situation toward the end of secondary oil extraction: theflooding water has formed a channel and flows through the channelwithout picking up further oil.

FIG. 3 Schematic illustration of surfactant flooding in a mineral oilformation: oil droplets released from the rock pores before (A) andafter (B) combination to a continuous oil bank.

FIG. 4 Schematic illustration of the progress of the continuous oil bankin the mineral oil formation. The oil bank absorbs new oil droplets inflow direction. Surfactant is released counter to the flow direction.

Regarding the invention, the following should be stated specifically:

The inventive surfactants are surfactants of the general formula R¹—Xwhere R¹ is a branched aliphatic C₁₇H₃₅-alkyl radical whose mean degreeof branching is from 2.8 to 3.7. The degree of branching is preferablyfrom 2.9 to 3.6, more preferably from 3.01 to 3.5, even more preferablyfrom 3.05 to 3.4 and, for example, about 3.1.

X is a hydrophilic group which imparts amphiphilic properties to themolecule. It may in principle be any hydrophilic groups which aresuitable for use as end groups in surfactants. The person skilled in theart is aware of appropriate hydrophilic groups.

The surfactants can be prepared proceeding from a branched aliphaticalcohol R¹—OH with a degree of branching of from 2.8 to 3.7, preferablyfrom 2.9 to 3.6, more preferably from 3.01 to 3.5, even more preferablyfrom 3.05 to 3.4, and, for example, about 3.1.

In this context, the term “degree of branching” is defined in a mannerknown in principle as the number of methyl groups in one molecule of thealcohol minus 1. The mean degree of branching is the statistical mean ofthe degrees of branching of all molecules of one sample. In other words,the alcohol R¹—OH used may be a mixture of different alcohols, andaccordingly the inventive surfactants may also be a mixture of differentsurfactants which have different aliphatic C₁₇H₃₅-alkyl radicals in eachcase.

The mean degree of branching can be determined by ¹H NMR spectroscopy asfollows: a sample of the alcohol is first subjected to a derivatizationwith trichloroacetyl isocyanate (TAI). This converts the alcohols to thecarbamic esters. The signals of the esterified primary alcohols are atδ=4.7 to 4.0 ppm, those of the esterified secondary alcohols (wherepresent) at about 5 ppm, and water present in the sample reacts with TAIto give carbamic acid. All methyl, methylene and methine protons arewithin the range from 2.4 to 0.4 ppm. The signals <1 ppm are assigned tothe methyl groups. The mean degree of branching (iso index) can becalculated from the spectrum thus obtained as follows:iso index=((F(CH₃)/3)/(F(CH₂—OH)/2))−1where F(CH₃) is the signal area corresponding to the methyl protons andF(CH₂—OH) is the signal area of the methylene protons in the CH₂—OHgroup.Provision of the Alcohols R¹—OH Used

The alcohols R¹—OH can in principle be synthesized by any desiredprocess, provided that they have the degree of branching described ineach case.

Alcohols R¹—OH can be obtained, for example, from a branched C₁₆-olefinby hydroformylation followed by hydrogenation of the resulting aldehydeto the alcohol. The performance of a hydroformylation and of thesubsequent hydrogenation is known in principle to those skilled in theart. The C₁₆-olefins used for this purpose can be prepared bytetramerizing butene.

The C₁₇-alcohol mixture can preferably be prepared by

-   a) providing a hydrocarbon feed material which comprises at least    one olefin having from 2 to 6 carbon atoms,-   b) subjecting the hydrocarbon feed material to an oligomerization    over a transition metal catalyst,-   c) subjecting the oligomerization product obtained in step b) to a    distillative separation to obtain an olefin stream enriched in    C₁₆-olefins,-   d) subjecting the olefin stream enriched in C₁₆-olefins which has    been obtained in step c) to a hydroformylation by reacting it with    carbon monoxide and hydrogen in the presence of a cobalt    hydroformylation catalyst and then to a hydrogenation.    Step a) Provision of a Hydrocarbon Mixture

Suitable olefin feed materials for step a) are in principle allcompounds which comprise from 2 to 6 carbon atoms and at least oneethylenically unsaturated double bond. In step a), preference is givento using an olefinic hydrocarbon mixture available in industry.

Preferred olefin mixtures obtainable on the industrial scale result fromhydrocarbon cleavage in mineral oil processing, for example by catalyticcracking, such as fluid catalytic cracking (FCC), thermocracking orhydrocracking with subsequent dehydrogenation. A preferred industrialolefin mixture is the C₄ cut. C₄ cuts are obtainable, for example, byfluid catalytic cracking or steamcracking of gas oil or by steamcrackingof naphtha. According to the composition of the C₄ cut, a distinction isdrawn between the overall C₄ cut (crude C₄ cut), the so-called RaffinateI obtained after 1,3-butadiene has been removed, and the Raffinate IIobtained after the isobutene removal. A further suitable industrialolefin mixture is the C₅ cut obtainable in naphtha cleavage. Olefinichydrocarbon mixtures having from 4 to 6 carbon atoms which are suitablefor use in step a) can also be obtained by catalytic dehydrogenation ofsuitable paraffin mixtures available on the industrial scale. Forexample, it is possible to prepare C₄ olefin mixtures from liquid gases(liquefied petroleum gas, LPG) and liquefiable natural gases (liquefiednatural gas, LNG). As well as the LPG fraction, the latter alsoadditionally comprise relatively large amounts of relatively highmolecular weight hydrocarbons (light naphtha) and are therefore alsosuitable for preparing C₅ and C₆ olefin mixtures. The preparation ofolefinic hydrocarbon mixtures which comprise monoolefins having from 4to 6 carbon atoms from LPG or LNG streams is possible by customaryprocesses known to those skilled in the art which, as well asdehydrogenation, generally also comprise one or more workup steps. Theseinclude, for example, the removal of at least a portion of the saturatedhydrocarbons present in the aforementioned olefin feed mixtures. Thesecan, for example, be used again to prepare olefin feed materials bycracking and/or dehydrogenation. The olefins used in step a) may,however, also comprise a proportion of saturated hydrocarbons whichbehave inertly with respect to the oligomerization conditions. Theproportion of these saturated components is generally at most 60% byweight, preferably at most 40% by weight, more preferably at most 20% byweight, based on the total amount of the olefins and saturatedhydrocarbons present in the hydrocarbon feed material.

In step a), preference is given to providing a hydrocarbon mixture whichcomprises from 20 to 100% by weight of C₄ olefins, from 0 to 80% byweight of C₅ olefins, from 0 to 60% by weight of C₆ olefins and from 0to 10% by weight of olefins other than the aforementioned olefins, basedin each case on the total olefin content.

Preference is given to providing, in step a), a hydrocarbon mixturewhich has a content of linear monoolefins of at least 80% by weight,more preferably at least 90% by weight and especially at least 95% byweight, based on the total olefin content. The linear monoolefins areselected from 1-butene, 2-butene, 1-pentene, 2-pentene, 1-hexene,2-hexene, 3-hexene and mixtures thereof. To establish the desired degreeof branching of the isoalkane mixture, it may be advantageous when thehydrocarbon mixture used in step a) comprises up to 20% by weight,preferably up to 5% by weight, especially up to 3% by weight, ofbranched olefins, based on the total olefin content.

Particular preference is given to providing a C₄ hydrocarbon mixture instep a).

The butene content, based on 1-butene, 2-butene and isobutene, of the C₄hydrocarbon mixture provided in step a) is preferably from 10 to 100% byweight, more preferably from 50 to 99% by weight and especially from 70to 95% by weight, based on the total olefin content. The ratio of1-butene to 2-butene is preferably within a range from 20:1 to 1:2,especially from about 10:1 to 1:1. The C₄ hydrocarbon mixture used instep a) preferably comprises less than 5% by weight, especially lessthan 3% by weight, of isobutene.

The provision of the olefinic hydrocarbons in step a) may comprise aremoval of branched olefins. Suitable removal processes are customaryremoval processes which are known from the prior art and are based ondifferent physical properties of linear and branched olefins or ondifferent reactivities which enable selective conversions. For example,isobutene can be removed from C₄ olefin mixtures, such as Raffinate I,by one of the following methods: molecular sieve separation, fractionaldistillation, irreversible hydration to tert-butanol, acid-catalyzedalcohol addition to a tertiary ether, for example methanol addition tomethyl tert-butyl ether (MTBE), irreversible catalyzed oligomerizationto di- and tri-isobutene or irreversible polymerization topolyisobutene. Such processes are described in K. Weissermel, H.-J.Arpe, Industrielle organische Chemie [Industrial Organic Chemistry], 4thedition, p. 76-81, VCH-Verlagsgesellschaft Weinheim, 1994, which isfully incorporated here by reference.

Preference is given to providing a Raffinate II in step a).

A Raffinate II suitable for use in the process has, for example, thefollowing composition: from 0.5 to 5% by weight of isobutane, from 5 to20% by weight of n-butane, from 20 to 40% by weight of trans-2-butene,from 10 to 20% by weight of cis-2-butene, from 25 to 55% by weight of1-butene, from 0.5 to 5% by weight of isobutene, and trace gases, forexample 1,3-butadiene, propene, propane, cyclopropane, propadiene,methylcyclopropane, vinylacetylene, pentenes, pentanes, in the region ofin each case not more than 1% by weight.

A particularly suitable Raffinate II has the following typicalcomposition:

i-butane: 3% by weight, n-butane: 15% by weight, i-butene: 2% by weight,butene-1: 30% by weight, butene-2-trans: 32% by weight, butene-2-cis:18% by weight.

When diolefins or alkynes are present in the olefin-rich hydrocarbonmixture, they can be removed therefrom to preferably less than 100 ppmbefore the oligomerization. They are preferably removed by selectivehydrogenation, for example according to EP-81 041 and DE-15 68 542, morepreferably by a selective hydrogenation down to a residual content ofbelow 50 ppm.

Oxygen compounds such as alcohols, aldehydes, ketones or ethers areappropriately also substantially removed from the olefin-richhydrocarbon mixture. To this end, the olefin-rich hydrocarbon mixturecan advantageously be passed over an adsorbent, for example a molecularsieve, especially one having a pore diameter of from >4 Å to 5 Å. Theconcentration of oxygen, sulfur, nitrogen and halogen compounds in theolefin-rich hydrocarbon mixture is preferably less than 1 ppm by weight,especially less than 0.5 ppm by weight.

Step b) Oligomerization

In the context of the preparation process described for C₁₇ alcohols,the term “oligomers” comprises dimers, trimers, tetramers, pentamers,and higher products from the formation reaction of the olefins used. Theoligomers are themselves olefinically unsaturated. Through suitableselection of the hydrocarbon feed material used for the oligomerizationand of the oligomerization catalyst, as described below, it is possibleto obtain an oligomerization product which comprises C₁₆ olefins whichcan be processed further advantageously to the C₁₇ alcohol mixture usedin accordance with the invention.

For the oligomerization in step b), it is possible to use a reactionsystem which comprises one or more, identical or different reactors. Inthe simplest case, a single reactor is used for the oligomerization instep b). However, it is also possible to use a plurality of reactorswhich each have identical or different mixing characteristics. Theindividual reactors can optionally be divided once or more than once byinternals. When two or more reactors form the reaction system, they canbe connected to one another as desired, for example in parallel or inseries. In a suitable embodiment, for example, a reaction system whichconsists of two reactors connected in series is used.

Suitable pressure-resistant reaction apparatus for the oligomerizationis known to those skilled in the art. It includes the generallycustomary reactors for gas-solid and gas-liquid reactions, for exampletubular reactors, stirred tanks, gas circulation reactors, bubblecolumns, etc., which may be divided by internals if appropriate.Preference is given to using tube bundle reactors or shaft ovens. When aheterogeneous catalyst is used for the oligomerization, it may bearranged in a single fixed catalyst bed or in a plurality of fixedcatalyst beds. It is possible to use different catalysts in differentreaction zones. However, preference is given to using the same catalystin all reaction zones.

The temperature in the oligomerization reaction is generally within arange from about 20 to 280° C., preferably from 25 to 200° C.,especially from 30 to 140° C. The pressure in the oligomerization isgenerally within a range from about 1 to 300 bar, preferably from 5 to100 bar and especially from 20 to 70 bar. When the reaction systemcomprises more than one reactor, the reactors may have identical ordifferent temperatures and identical or different pressures. Forexample, in the second reactor of a reactor cascade, a highertemperature and/or a higher pressure than in the first reactor can beestablished, for example in order to achieve a maximum conversion.

In a specific embodiment, the temperature and pressure values used forthe oligomerization are selected such that the olefinic feed material ispresent in the liquid or supercritical state.

The reaction in step b) is preferably performed adiabatically. This termis understood below in the technical sense and not in the physiochemicalsense. Thus, the oligomerization reaction generally proceedsexothermically, such that the reaction mixture, as it flows through thereaction system, for example a catalyst bed, experiences an increase intemperature. An adiabatic reaction regime is understood to mean aprocedure in which the amount of heat released in an exothermic reactionis absorbed by the reaction mixture in the reactor and no cooling bycooling apparatus is employed. The heat of reaction is thus removed fromthe reactor with the reaction mixture, apart from a residual fractionwhich is released to the environment by natural heat conduction and heatemission from the reactor.

For the oligomerization in step b), a transition metal catalyst is used.The catalysts are preferably heterogeneous catalysts. Preferredcatalysts for the reaction in step a) which are known to bring about alow degree of oligomer branching are known in general terms to thoseskilled in the art. These include the catalysts described in CatalysisToday, 6, 329 (1990), especially pages 336-338, and those described inDE-A-43 39 713 (=WO-A 95/14647) and DE-A-199 57 173, which are herebyexplicitly incorporated by reference. A suitable oligomerization processin which the feed stream used for the oligomerization is divided and fedto at least two reaction zones operated at different temperatures isdescribed in EP-A-1 457 475, which is likewise incorporated byreference.

Preference is given to using an oligomerization catalyst which comprisesnickel. Preference is given to heterogeneous catalysts which comprisenickel oxide. The heterogeneous nickel-comprising catalysts used mayhave different structures. In principle, unsupported catalysts andsupported catalysts are suitable. The latter are used with preference.The support materials may, for example, be silica, alumina, aluminosilicates, alumino silicates with layer structures, and zeolites such asmordenite, faujasite, zeolite X, zeolite Y and ZSM-5, zirconium oxidewhich has been treated with acids, or sulfated titanium dioxide.Particularly suitable catalysts are precipitation catalysts which areobtainable by mixing aqueous solutions of nickel salts and silicates,for example sodium silicate with nickel nitrate, and if appropriatealuminum salts, such as aluminum nitrate, and calcination. It is alsopossible to use catalysts which are obtained by intercalating Ni²⁺ ionsby ionic exchange in natural or synthetic sheet silicates, such asmontmorillonites. Suitable catalysts can also be obtained byimpregnating silica, alumina, or alumino silicates with aqueoussolutions of soluble nickel salts, such as nickel nitrate, nickelsulfate or nickel chloride, and subsequent calcination.

Catalysts comprising nickel oxide are preferred. Particular preferenceis given to catalysts which consist essentially of NiO, SiO₂, TiO₂and/or ZrO₂, and if appropriate Al₂O₃. Most preferred is a catalystwhich comprises, as essential active constituents, from 10 to 70% byweight of nickel oxide, from 5 to 30% by weight of titanium dioxideand/or zirconium dioxide, from 0 to 20% by weight of aluminum oxide and,as the remainder, silicon dioxide. Such a catalyst is obtainable byprecipitating the catalyst material at pH 5 to 9 by adding an aqueoussolution comprising nickel nitrate to an alkali metal waterglasssolution which comprises titanium dioxide and/or zirconium dioxide,filtering, drying and heat treating at from 350 to 650° C. For thepreparation of these catalysts, reference is made specifically to DE-4339 713. The disclosure of this publication and the prior art citedtherein are fully incorporated by reference.

In a further embodiment, the catalyst used in step b) is a nickelcatalyst according to DE-A-199 57 173. This is essentially aluminumoxide which has been contacted with a nickel compound and a sulfurcompound. A molar ratio of sulfur to nickel in the range from 0.25:1 to0.38:1 is preferably present in the finished catalyst.

The catalyst is preferably present in piece form, for example in theform of tablets, for example having a diameter of from 2 to 6 mm and aheight of from 3 to 5 mm, rings with, for example, external diameterfrom 5 to 7 mm, height from 2 to 5 mm and hole diameter from 2 to 3 mm,or extrudates of different length of diameter of, for example, from 1.5to 5 mm. Such shapes are obtained in a manner known per se by tabletingor extrusion, usually using a tableting assistant, such as graphite orstearic acid.

In step b), preference is given to using a C₄ hydrocarbon mixture forthe oligomerization to obtain an oligomerization product which comprisesfrom 1 to 25% by weight, preferably from 2 to 20% by weight, especiallyfrom 3 to 15% by weight, of C₁₆ olefins based on the total weight of theoligomerization product.

Step c) Distillation

A C₁₆ olefin fraction is isolated in one or more separation steps fromthe reaction effluent of the oligomerization reaction. The distillativeseparation of the oligomerization product obtained in step b) to obtainan olefin stream enriched in C₁₆ olefins can be effected continuously orbatchwise (discontinuously).

Suitable distillation apparatus is the customary apparatus known tothose skilled in the art. This includes, for example, distillationcolumns such as tray columns which may, if desired, be equipped withinternals, valves, side draws, etc., evaporators such as thin-filmevaporators, falling-film evaporators, wiped-blade evaporators, Sambayevaporators, etc., and combinations thereof. Preference is given toisolating the C₁₆ olefin fraction by fractional distillation.

The distillation itself can be effected in one distillation column or ina plurality of distillation columns coupled to one another.

The distillation column or the distillation columns used can be realizedin a design known per se (see, for example, Sattler, ThermischeTrennverfahren [Thermal Separating Methods], 2nd edition, 1995,Weinheim, p. 135ff; Perry's Chemical Engineers Handbook, 7th edition1997, New York, section 13). The distillation columns used may compriseseparating internals, such as separating trays, for example perforatedtrays, bubble-cap trays or valve trays, structured packings, for examplesheet metal or fabric packings, or random packings. In the case of useof tray columns with downcomers, the downcomer residence time ispreferably at least 5 seconds, more preferably at least 7 seconds. Thespecific design and operating data, like the number of stages and thereflux ratio needed in the column(s) used, can be determined by theperson skilled in the art by known methods.

In a preferred embodiment, a combination of two columns is used fordistillation. In this case, the olefin oligomers having fewer than 16carbon atoms (i.e. the C₈ and C₁₂ oligomers when a C₄ hydrocarbonmixture is used) are withdrawn as the top product from the first column.The olefin stream enriched in C₁₆ olefins is obtained as the top productof the second column. Olefin oligomers with more than 16 carbon atoms(i.e. the C₂₀, C₂₄ and higher oligomers when a C₄ hydrocarbon mixture isused) are obtained as the bottom product of the second column.

Suitable evaporators and condensers are likewise apparatus types knownper se. The evaporator used may be a heatable vessel customary for thispurpose, or an evaporator with forced circulation, for example afalling-film evaporator. When two distillation columns are used for thedistillation, they may be provided with identical or differentevaporators and condensers.

The bottom temperatures which occur in the distillation are preferablyat most 300° C., more preferably at most 250° C. To maintain thesemaximum temperatures, the distillation can, if desired, be carried outunder a suitable vacuum.

In step c), preference is given to isolating an olefin stream enrichedin C₁₆ olefins which has a content of olefins having 16 carbon atoms ofat least 95% by weight, more preferably at least 98% by weight,especially at least 99% by weight, based on the total weight of theolefin stream enriched in C₁₆ olefins. More especially, in step c), anolefin stream enriched in C₁₆ olefins which consists essentially (i.e.to an extent of more than 99.5% by weight) of olefins having 16 carbonatoms is isolated.

Step d) Hydroformylation

To prepare an alcohol mixture, the olefin stream enriched in C₁₆ olefinsis hydroformylated and then hydrogenated to C₁₇ alcohols. The alcoholmixture can be prepared in one stage or in two separate reaction steps.An overview of hydroformylation processes and suitable catalysts can befound in Beller et al., Journal of Molecular Catalysis A 104 (1995), p.17-85.

It is critical for the synthesis of the alcohol mixture described thatthe hydroformylation is effected in the presence of a cobalthydroformylation catalyst. The amount of the hydroformylation catalystis generally from 0.001 to 0.5% by weight, calculated as cobalt metal,based on the amount of the olefins to be hydroformylated.

The reaction temperature is generally in the range from about 100 to250° C., preferably from 150 to 210° C. The reaction can be performed atan elevated pressure of from about 10 to 650 bar, preferably from 25 to350 bar.

In a suitable embodiment, the hydroformylation is effected in thepresence of water; however, it can also be carried out in the absence ofwater.

Carbon monoxide and hydrogen are typically used in the form of amixture, known as synthesis gas. The composition of the synthesis gasused may vary within a wide range. The molar ratio of carbon monoxideand hydrogen is generally from about 2.5:1 to 1:2.5. A preferred ratiois about 1:1.

The hydroformylation-active cobalt catalyst is HCo(CO)₄. The catalystcan be preformed outside the hydroformylation reactor, for example froma cobalt(II) salt in the presence of synthesis gas, and be introducedinto the hydroformylation reactor together with the C₁₆ olefins and thesynthesis gas. Alternatively, the catalytically active species can beformed from catalyst precursors actually under the hydroformylationconditions, i.e. in the reaction zone. Suitable catalyst precursors arecobalt(II) salts, such as cobalt(II) carboxylates, e.g. cobalt(II)formate or cobalt(II) acetate; and also cobalt(II) acetylacetonate orCo₂(CO)₈.

The cobalt catalyst dissolved homogeneously in the reaction medium cansuitably be removed from the hydroformylation product, in which case thereaction effluent from the hydroformylation initially treated withoxygen or air in the presence of an acidic aqueous solution. Thisoxidatively destroys the cobalt catalyst to form cobalt(II) salts. Thecobalt(II) salts are water-soluble and can be removed from the reactioneffluent by extraction with water. They can generally be used again toprepare a hydroformylation catalyst and be recycled into thehydroformylation process.

To continuously perform the hydroformylation, the procedure may be, forexample, (i) to intimately contact an aqueous cobalt(II) salt solutionwith hydrogen and carbon monoxide to form a hydroformylation-activecobalt catalyst; (ii) to intimately contact the aqueous phase comprisingthe cobalt catalyst in a reaction zone with the olefins and hydrogen andcarbon monoxide, the cobalt catalyst being extracted into the organicphase and the olefins being hydroformylated; and (iii) to treat theeffluent from the reaction zone with oxygen, the cobalt catalyst beingdecomposed to form cobalt(II) salts, the cobalt(II) salts beingreextracted into the aqueous phase and the phases being separated. Theaqueous cobalt(II) salt solution is then recycled into the process.Suitable cobalt(II) salts include in particular cobalt(II) acetate,cobalt(II) formate and cobalt(II) ethylhexanoate. Advantageously, theformation of the cobalt catalyst, the extraction of the cobalt catalystinto the organic phase and the hydroformylation of the olefins can beeffected in one step by intimately contacting the aqueous cobalt(II)salt solution, the olefins and if appropriate the organic solvent, andalso hydrogen and carbon monoxide, in the reaction zone underhydroformylation conditions, for example by means of a mixing nozzle.

The crude aldehydes or aldehyde/alcohol mixtures obtained in thehydroformylation can, if desired, be isolated and if appropriatepurified before the hydrogenation by customary processes known to thoseskilled in the art. In general, the product mixture obtained afterremoval of the hydroformylation catalyst can be used in thehydrogenation without further workup.

Hydrogenation

For the hydrogenation, the reaction mixtures obtained in thehydroformylation are reacted with hydrogen in the presence of ahydrogenation catalyst.

Suitable hydrogenation catalysts are generally transition metals, forexample Cr, Mo, W, Fe, Rh, Co, Ni, Pd, Pt, Ru etc., or mixtures thereof,which can be applied to supports, for example activated carbon, aluminumoxide, kieselguhr, etc., to increase the activity and stability. Toincrease the catalytic activity, Fe, Co and preferably Ni, including inthe form of Raney catalysts, can be used in the form of metal spongewith a very high surface area. For the preparation of the inventivesurfactant alcohols, preference is given to using a Co/Mo catalyst.Depending on the activity of the catalyst, the oxo aldehydes arehydrogenated preferably at elevated temperatures and elevated pressure.The hydrogenation temperature is preferably from about 80 to 250° C. Thepressure is preferably from about 50 to 350 bar.

The reaction mixture obtained after the hydrogenation can be worked upby customary purification processes known to those skilled in the art,especially by fractional distillation, to obtain a C₁₇ alcohol mixturewith the degree of branching outlined at the outset in pure form.

The C₁₇ alcohol mixture obtained by the process described preferably hasa content of alcohols having 17 carbon atoms of at least 95% by weight,more preferably at least 98% by weight, especially at least 99% byweight, based on the total weight of the C₁₇ alcohol mixture. It isespecially a C₁₇ alcohol mixture which consists essentially (i.e. to anextent of more than 99.5% by weight, especially to an extent of morethan 99.9% by weight) of alcohols having 17 carbon atoms.

Surfactants R¹—X

The hydrophilic X groups of the surfactant R¹—X may be anionic,nonionic, cationic or betainic groups. They are preferably anionic ornonionic groups. Examples of preferred X groups comprise sulfonategroups, polyoxyalkylene groups, anionically modified polyoxyalkylenegroups, glucoside groups or amine oxide groups. Particular preference isgiven to surfactants with polyoxyalkylene groups and anionicallymodified polyoxyalkylene groups. Anionically modified polyoxyalkylenegroups preferably have terminal sulfonate, terminal carboxylate orterminal sulfate groups. The polyoxyalkylene groups may comprise from 1to 50 oxyalkylene groups, preferably from 1 to 40, preferably ethoxygroups and/or propoxy groups. In addition, even higher alkyleneoxygroups may also be present. Preferably at least 50% of the oxyalkylenegroups present are ethoxy groups. Such surfactants R¹—X can be preparedproceeding from the alcohols R¹—OH by methods known in principle tothose skilled in the art. The X group may also be OH, i.e. the alcoholR¹—OH itself shall also be considered as a surfactant in the context ofthis invention.

Description of Preferred Surfactants R¹—X

Surfactants R¹—X preferred for use in tertiary mineral oil extractionare described below.

In a preferred embodiment of the invention, the inventive surfactantsare those selected from the group of alkyl alkoxylates (A), alkyl ethersulfonates (B), alkyl ether carboxylates (C), alkyl ether sulfates (D),alkylpolyglucosides (E) and/or alkylamine oxides (F).

Alkyl Alkoxylates (A)

The alkyl alkoxylates (A) have the general formula (I)R¹O—(CH₂CH(R²)O)_(n)(CH₂CH₂O)_(m)—H  (I).

The alkyl alkoxylates (A) comprise n alkoxy groups of the generalformula —CH₂CH(R²)O— and methoxy groups —CH₂CH₂O—. The formula of thealkoxy group shall also include units of the formula —CH(R²)CH₂O—, i.e.alkoxy groups incorporated in inverse orientation into the surfactant,and it will be appreciated that both arrangements may also be present inone surfactant molecule. R² comprises straight-chain, branched,aliphatic or aromatic hydrocarbon radicals having from 1 to 10 carbonatoms, and one surfactant molecule may also have a plurality ofdifferent R² radicals. R² is preferably a methyl, ethyl, n-propyl and/orphenyl group, and more preferably a methyl group, i.e. the alkoxy groupis a propoxy group.

The numbers n and m are based in a known manner on the mean of thealkoxy and ethoxy groups present in the surfactant, and it will beappreciated that the mean need not be a natural number but may also beany rational number. The number n is from 0 to 15, preferably from 0 to7 and more preferably from 0 to 5, and m is from 1 to 20, preferablyfrom 2 to 15 and more preferably from 5 to 14. The sum k=n+m is from 1to 35, preferably from 2 to 20 and more preferably from 5 to 15.Additionally preferably, m>n, i.e., in the preferred variant, the numberof ethoxy groups is greater than that of alkoxy groups.

The arrangement of the alkoxy groups and ethoxy groups in the surfactant(I)—where both types of groups are present—may be random or alternating,or a block structure may be present. It is preferably a block structurein which the alkoxy and ethoxy groups are actually arranged in theR¹O-alkoxy block-ethoxy block-H sequence.

The alkyl alkoxylates (A) can be prepared in a manner known in principleby alkoxylating the alcohol R¹—OH. The performance of alkoxylations isknown in principle to those skilled in the art. It is likewise known tothose skilled in the art that the reaction conditions, especially theselection of the catalyst, can influence the molecular weightdistribution of the alkoxylates.

The alkyl alkoxylates (A) can be prepared, for example, bybase-catalyzed alkoxylation. To this end, the alcohol R¹—OH can beadmixed in a pressure reactor with alkali metal hydroxides, preferablypotassium hydroxide, or with alkali metal alkoxides, for example sodiummethoxide. By means of reduced pressure (for example <100 mbar) and/oran increase in the temperature (from 30 to 150° C.), it is possible todraw off water still present in the mixture. The alcohol is then presentas the corresponding alkoxide. This is followed by inertization withinert gas (e.g. nitrogen) and addition of the alkylene oxide(s) stepwiseat temperatures of from 60 to 180° C. up to a pressure of max. 10 bar.At the end of the reaction, the catalyst can be neutralized by addingacid (e.g. acetic acid or phosphoric acid) and can be filtered off ifrequired. Alkyl alkoxylates prepared by means of KOH catalysis generallyhave a relatively broad molecular weight distribution.

In a preferred embodiment of the invention, the alkyl alkoxylates (A)are synthesized by means of techniques known to those skilled in the artwhich lead to narrower molecular weight distributions than in the caseof base-catalyzed synthesis. To this end, the catalysts used may, forexample, be double hydroxide clays, as described in DE 43 25 237 A1. Thealkoxylation can more preferably be effected using double metal cyanidecatalysts (DMC catalysts). Suitable DMC catalysts are disclosed, forexample, in DE 102 43 361A1, especially paragraphs [0029] to [0041] andthe literature cited therein. For example, catalysts of the Zn—Co typecan be used. To perform the reaction, alcohol R¹—OH can be admixed withthe catalyst, and the mixture dewatered as described above and reactedwith the alkylene oxides as described. Typically, not more than 250 ppmof catalyst based on the mixture are used, and the catalyst can remainin the product owing to this small amount. Inventive surfactantsprepared by means of DMC catalysis are notable in that they result in abetter lowering of the interfacial tension in the water-mineral oilsystem than products prepared by means of KOH catalysis.

Alkyl alkoxylates (A) can additionally also be prepared byacid-catalyzed alkoxylation. The acids may be Bronsted or Lewis acids.To perform the reaction, alcohol R¹—OH can be admixed with the catalyst,and the mixture can be dewatered as described above and reacted with thealkylene oxides as described. At the end of the reaction, the catalystcan be neutralized by adding a base, for example KOH or NaOH, and befiltered off if required. The selection of the catalyst allows thestructure of the hydrophilic X group to be influenced. While the alkoxyunits are incorporated into the alkyl alkoxylate predominantly in theorientation reproduced in formula (Ia) in the case of basic catalysis,the units are incorporated in greater portions in the orientation (Ib)in the case of acidic catalysis.

Alkyl Ether Sulfonates (B)

The alkyl ether sulfonates (B) derive from the alkyl alkoxylates (A) andadditionally have a terminal sulfonate group. The alkyl ether sulfonates(B) have the general formula (II)R¹O—(CH₂CH(R²)O)_(n′)(CH₂CH₂O)_(m′)—R³—SO₃M  (II)where R² is as defined above. In formula (II), M is H⁺ or a k-valentcounterion 1/x Y^(x+). x here is the charge of the counterion. Thecounterion is preferably a monovalent counterion such as NH₄ ⁺—,ammonium ions with organic radicals or alkali metal ions. Y ispreferably Li⁺, Na⁺ and K⁺, and particular preference is given to Na⁺.The alkyl ether sulfonate may thus be present as the free acid or as asalt thereof.

The number n′ here is from 0 to 15, preferably from 1 to 10, and m′ isfrom 1 to 20, preferably from 2 to 15 and more preferably from 5 to 14.The sum k′=n′+m′ here is from 1 to 35, preferably from 1 to 20 and morepreferably from 1 to 15. Additionally preferably, m′>n′, i.e. the numberof ethoxy groups is greater than that of the alkoxy groups.

As defined above, the arrangement of the alkoxy and ethoxy groups may berandom or alternating, or a block structure may be present. It ispreferably a block structure in which the alkoxy and propoxy groups areactually arranged in the R¹O-alkoxy block-ethoxy block-R³—SO₃M sequence.

The R³ group which links the alkoxy group to the sulfonate group is adivalent hydrocarbon group having from 2 to 12 carbon atoms, preferablyfrom 2 to 4 carbon atoms, which may optionally have functional groups assubstituents. It is preferably a group selected from the group of1,2-ethylene groups —CH₂—CH₂—, 1,2-propylene groups —CH₂—CHR²— or—CH(R²)—CH₂— or 1,3-propylene groups —CH₂—CH(R⁴)—CH₂—, where R² is asdefined at the outset and R⁴ is H or OH.

The inventive alkyl ether sulfonates (B) can be prepared using the alkylalkoxylates (A) as the starting material. The conversion to thesulfonate can be effected, for example, by substituting the OH group ofthe alkoxylate for Cl using phosgene or thionyl chloride. The reactioncan be undertaken in the presence of a solvent, for examplechlorobenzene. HCl released and CO₂ or SO₂ released can advantageouslybe removed from the system by stripping with nitrogen, such that ethercleavage is suppressed. The alkyl alkoxychlorine compound is thenreacted with an aqueous solution of sodium sulfite, which substitutesthe chloride for sulfite to obtain the alkyl ether sulfonate. Thesubstitution can be undertaken in the presence of a phase mediator (forexample C₁- to C₈-alcohols) at a temperature of 100-180° C. andpressure. According to whether an ethoxy group or an alkoxy group ispresent as the terminal group in the alkyl alkoxylate (A), the alkylether sulfonate (B) has, as the terminal —R³—SO₃M group, a —CH₂CH₂—SO₃Mor —CH(R²)—CH₂—SO₃M or —CH₂—CH(R²)—SO₃M group. In this synthesisvariant, k′=k−1. An alternative to the chlorination is the sulfation ofthe alkyl alkoxylates (A) with SO₃ in a falling-film reactor andsubsequent neutralization with NaOH. The alkyl ether sulfate formed canbe converted to the alkyl ether sulfonate (B) by means of nucleophilicsubstitution of the sulfate group for sodium sulfite analogously to theabove description.

The alkyl ether sulfonates (B) can alternatively be obtained by addingvinylsulfonic acid onto the alkyl alkoxylate (A). Details on thissubject are described, for example, in EP 311 961 A1. In this case, analkyl ether sulfonate (B) with a terminal —CH₂CH₂—SO₃M group isobtained, where k′=k.

Alkyl ether sulfonates (B) with a terminal —CH₂—CH₂—CH₂—SO₃M group (i.e.R⁴═H) can be obtained by reacting the alkyl alkoxylate with1,3-propanesultone. Alkyl ether sulfinates (B) with a terminal—CH₂—CH(OH)—CH₂—SO₃M group are obtainable by the reaction of theappropriate alkyl alkoxylate (A) with epichlorohydrin and subsequentnucleophilic substitution of the chloride group for sodium sulfite. Inboth cases, k′=k.

Alkyl Ether Carboxylates (C)

The alkyl ether carboxylates (C) derive from the alkyl alkoxylates (A)and additionally have a terminal carboxylate group. Preferred alkylether carboxylates (C) have the general formula (III)R¹O—(CH₂CH(R²)O)_(n″)(CH₂CH₂O)_(m″)—R⁵—COOM  (III)where R² and M are each as defined above.

The number n″ here is from 0 to 15, preferably from 1 to 10, and m″ isfrom 1 to 20, preferably from 2 to 15 and more preferably from 5 to 14.The sum k″=n″+m″ here is from 1 to 35, preferably from 1 to 20 and morepreferably from 1 to 15. Additionally preferably, m″>n″, i.e. the numberof ethoxy groups is greater than that of alkoxy groups.

The alkyl ether carboxylate (C) may thus be present as the free acid oras a salt thereof. As defined above, the arrangement of the alkoxy andethoxy groups may be random or alternating, or a block structure may bepresent. It is preferably a block structure in which the alkoxy andpropoxy groups are actually arranged in the R¹O-alkoxy block-ethoxyblock-R⁵—COOM sequence.

The R⁵ group which links the alkoxy group to the carboxylate group is adivalent hydrocarbon group having from 1 to 12 carbon atoms, preferablyfrom 1 to 3 carbon atoms. It is preferably a methylene group —CH₂—, a1,2-ethylene group —CH₂—CH₂— or a 1,2-propylene group —CH₂—CH(CH₃)—.

The inventive alkyl ether carboxylates (C) can be prepared using thealkyl alkoxylates (A) as the starting material. These can be convertedby oxidizing the alkoxylate to the corresponding alkyl ethercarboxylates (C). Suitable oxidizing agents for this purpose are inprinciple all oxidizing agents, if appropriate in conjunction withsuitable catalysts which can oxidize the terminal OH group of the alkylalkoxylate (A) to the COOH group without oxidizing other parts of themolecule to a high degree. The oxidation can be undertaken, for example,with the aid of air or oxygen using a noble metal catalyst (for examplea catalyst based on palladium). In this synthesis variant, a terminal—CH₂—COOM group is obtained and k′=k−1.

In a further embodiment of the invention, the inventive alkyl ethercarboxylates (C) can also be prepared by adding (meth)acrylic acid or a(meth)acrylic ester onto an alkyl alkoxylate (A) by means of a Michaeladdition. If the esters are used, they are hydrolyzed after theaddition. These synthesis variants afford—according to whether acrylicacid or (meth)acrylic acid or esters thereof have been used—terminal—CH₂—CH₂—COOM or —CH₂—CH(CH₃)—COOM groups and k″=k.

Alkyl Ether Sulfates (D)

The alkyl ether sulfates (D) derive from the alkyl alkoxylates (A) andadditionally have a terminal sulfate group. The alkyl ether sulfates (D)have the general formula (IV)R¹O—(CH₂CH(R²)O)_(m′″)(CH₂CH₂O)_(m′″)—SO₃M  (IV)where R² is as defined above. In formula (IV), M is H⁺ or a k-valentcounterion 1/x Y^(x+). x here is the charge of the counterion. It ispreferably a monovalent counterion, such as NH₄ ⁺—, ammonium ions withorganic radicals or alkali metal ions. Y is preferably Li⁺, Na⁺ and K⁺,and particular preference is given to Na⁺. The alkyl ether sulfate maythus be present as the free acid or as a salt thereof.

The number n′″ here is from 0 to 15, preferably from 1 to 10, and m′″ isfrom 1 to 20, preferably from 2 to 15 and more preferably from 5 to 14.The sum k′″=n′″+m′″ here is from 1 to 35, preferably from 1 to 20 andmore preferably from 1 to 15. Additionally preferably, m′″>n′″, i.e. thenumber of ethoxy groups is greater than that of alkoxy groups.

As defined above, the arrangement of the alkoxy and ethoxy groups may berandom or alternating, or a block structure may be present. It ispreferably a block structure in which the alkoxy and propoxy groups areactually arranged in the R¹O-alkoxy block-ethoxy block —SO₃M sequence.

The inventive alkyl ether sulfates (D) can be prepared using the alkylalkoxylates (A) as the starting material. The conversion to the sulfatecan be effected, for example, by adding the OH group of the alkoxylateonto sulfur trioxide and then neutralizing with, for example, sodiumhydroxide solution. This can be carried out, for example, in afalling-film reactor.

Alkylpolyglucosides (E)

The alkylpolyglucosides (E) have a polyglucoside group as the terminalgroup. Preferred alkylpolyglucosides (E) have the following formula (V)

I here is from 0 to 2, where I is the mean of the distribution. Thealkylpolyglucosides (E) can be prepared in a manner known in principle,by converting glucose to the corresponding butyl acetal with the aid ofan acidic catalyst, for example para-toluenesulfonic acid, andn-butanol. The water of reaction formed can be removed from the reactionmixture by applying reduced pressure. Thereafter, the alcohol R¹—OH isadded and the transacetalization is propelled by distillatively removingthe butanol from the equilibrium. The acidic catalyst can be neutralizedat the end of the reaction by adding base, for example NaOH or KOH.

Alkylamine Oxides (F)

The alkylamine oxides (F) have the general formula (VI)

R⁶ and R⁷ are each independently methyl or hydroxyethyl radicals. Theamine oxides (F) can be prepared in a manner known in principle byconverting the alcohol R¹—OH or its precursor, the aldehyde, to thecorresponding tertiary amine in a catalytic reductive amination withN,N-dimethylamine or diethanolamine and water. The amine oxide cansubsequently be obtained therefrom by adding hydrogen peroxide.

Use for Tertiary Mineral Oil Extraction

The inventive surfactants R¹—X can preferably be used for tertiarymineral oil extraction. By significantly lowering the interfacialtension between oil and water, they bring about particularly goodmobilization of the crude oil in the mineral oil formation.

To this end, they are injected in the form of a suitable formulationinto the mineral oil deposit through at least one injection bore, andcrude oil is withdrawn from the deposit through at least one productionbore. In this connection, the term “crude oil” of course does not justmean single-phase oil, but the term also includes the usual crudeoil-water emulsions. In general, a deposit is provided with severalinjection bores and with several production bores. After the injectionof the surfactant formulation, the so-called “surfactant flooding”, thepressure can be maintained by injecting water into the formation (“waterflooding”), or preferably a higher-viscosity aqueous solution of apolymer with high thickening action (“polymer flooding”). However,techniques in which the surfactants are first allowed to act on theformation are also known. The person skilled in the art is aware ofdetails of the technical performance of “surfactant flooding”, “waterflooding” and “polymer flooding”, and employs an appropriate techniqueaccording to the type of deposit.

The inventive surfactants are preferably used in aqueous formulation. Aswell as water, the formulations may comprise, as solvents, optionallynot more than 50% by weight, preferably not more than 20% by weight, ofwater-miscible alcohols.

For tertiary mineral oil extraction, it is possible in each case to useonly one of the inventive surfactants R¹—X. However, preference is givento using a formulation which comprises at least two differentsurfactants, in which case at least one of which is a surfactant R¹—X.

The surfactant R¹—X may be used here as a surfactant or else as acosurfactant. “Cosurfactant”, also referred to as “secondarysurfactant”, is understood in a manner known in principle to mean asurfactant which is added in a small amount to other surfactants orsurfactant mixtures in order to improve their profile of properties bysynergistic action. The amount of all surfactants R¹—X together based onthe total amount of all surfactants used in a surfactant mixture isdetermined by the person skilled in the art according to the type ofproperties desired. The amount of surfactants R¹—X is generally from 1to 99% by weight based on the total amount of all surfactants in themixture. The amount is preferably from 10 to 95% by weight.

Examples of further surfactants which can be used in addition to thesurfactants R¹—X comprise anionic surfactants, especially organicsulfonates, for example olefinsulfonates or alkylarylsulfonates,nonionic surfactants or anionic surfactants which are prepared byanionic modification of nonionic surfactants, for example ethersulfates, ether sulfonates or ether carboxylates, or alkylpolyols and/oralkylpolyglucosides. In addition, it is also possible to use amineoxides, surfactants with ammonium groups or betaines.

In addition to the surfactants, the formulations may also comprisefurther components, for example have C₁- to C₈-alcohols and/or basicsalts (so-called “alkali surfactant flooding”). Such additives can beused, for example, to reduce retention in the formation.

Mixtures which are preferred for tertiary mineral oil extraction andcomprise surfactants R¹—X are described below.

In a preferred embodiment of the invention, for tertiary mineral oilextraction, a mixture (M) of at least one nonionic surfactant (M1) andat least one anionic surfactant (M2) may be used, in which case at leastone of the two surfactants is a surfactant R¹—X. The anionic surfactant(M2) is more preferably an anionically modified, nonionic surfactant,especially a surfactant modified with sulfonate groups and/orcarboxylate groups and/or sulfate groups. Such mixtures are particularlysuitable for use in high-salinity deposits. For use, the mixtures may,as described above, preferably be formulated with suitable solvents ormixtures of solvents.

Additionally preferred are mixtures of at least one surfactant (M1′)with nonionic behavior and at least one surfactant (M2′) with ionicbehavior. This is understood in each case to mean surfactants in whichthe X group comprises both ionic and nonionic components and in which,according to the type and/or use conditions, nonionic behavior or ionicbehavior dominates. Examples of such surfactants comprise theabovementioned alkyl ether sulfonates, alkyl ether carboxylates andalkyl ether sulfates. A typical nonionic surfactant with polyether unitsbehaves more hydrophobically with increasing temperature in anoil-water-surfactant system. Such surfactants initially form anoil-in-water emulsion at relatively low temperatures, i.e. an emulsionof oil in a continuous water phase. When the temperature is increased,there is finally a phase transition to a water-in-oil emulsion, i.e. anemulsion of water in a continuous oil phase. This transition can bemonitored, for example, by a conductivity meter. The transition from acontinuous water phase to a discontinuous water phase is associated witha significant decline in the conductivity. Surfactants which behaveionically have the reverse behavior and become more hydrophilic withincreasing temperature. A water-in-oil emulsion is thus converted withincreasing temperature to an oil-in-water emulsion, which can likewisebe monitored readily with a conductivity meter.

The mixture is preferably a mixture (M) which comprises, as components,at least one alkyl alkoxylate (A) and/or an alkyl ether sulfonate (B)and/or alkyl ether sulfate (D). Additionally preferred is a mixturewhich comprises an alkyl ether sulfonate (B) in a mixture with an alkylether carboxylate (C), especially a mixture of an alkyl alkoxylate (A),an alkyl ether sulfonate (B) and an alkyl ether carboxylate (C).

Suitable mixture components in addition to the inventive surfactants areparticularly surfactants of the general formula R⁸—X where R⁸ is analiphatic or araliphatic C₁₆ to C₂₀ hydrocarbon radical, preferably aC₁₆ to C₁₈ hydrocarbon radical. A preferred radical should have a degreeof branching of less than 2, preferably of less than 1, and should morepreferably be linear. The hydrocarbon radicals may, for example, be4-dodecylphenyl radicals, or be hexadecyl, heptadecyl or octadecylradicals. The X radical is a hydrophilic group as defined above,preferably an X radical selected from the group of sulfonate groups,polyoxyalkylene groups, anionically modified polyoxyalkylene groups,glucoside groups or amine oxide groups.

More preferably, the surfactants R⁸—X may be alkyl alkoxylates of thegeneral formulaR⁸—(CH₂CH(R²)O)_(n)(CH₂CH₂O)_(m)—H  (VII)where the indices are each as defined above. Additionally preferably,they may be alkyl ether sulfonates of the general formulaR⁸O—(CH₂CH(R²)O)_(n′)(CH₂CH₂O)_(m′)—R³—SO₃M  (VIII)where the indices are likewise as defined above. Mixtures of thesurfactants R¹—X and R⁸—X can be prepared in a particularly simplemanner by starting the alkoxylation from a mixture of the alcohols R¹—OHand R⁸—OH and using the mixture of these alcohols as described above.

In a further preferred embodiment, the mixture (M), as well ascomponents (M1) and (M2), also comprises a polymeric cosurfactant (M3).The amount of the cosurfactant (M3) is not more than 49.9% by weightbased on the total amount of all surfactants (M1), (M2) and (M3) used.The amount is preferably from 1 to 10% by weight. With such polymericcosurfactants, it is advantageously possible to reduce the amount ofsurfactant needed to form a microemulsion. Such polymeric cosurfactantsare therefore also referred to as “microemulsion boosters”.

The polymeric cosurfactants (M3) are amphiphilic block copolymers whichcomprise at least one hydrophilic block and at least one hydrophobicblock. They preferably have molecular masses M_(n) of from 1000 to 50000 g/mol. The hydrophilic blocks and the hydrophobic blocks shouldgenerally have at least a molar mass of in each case 500 g/mol,preferably 750 g/mol and more preferably 1000 g/mol. The hydrophobic andhydrophilic blocks here can be joined together in various ways. Theymay, for example, be two-block copolymers or be multiple blockcopolymers in which the hydrophobic and hydrophilic blocks are arrangedin alternation. The polymers may be linear, branched or star-shaped, orthey may also be a comb polymer which has a main chain and one or moreside chains joined thereto.

Preference is given to block copolymers which have, as hydrophilicblocks, polyethylene oxide blocks or random polyethyleneoxide-polypropylene oxide blocks, where the propylene oxide contentshould not exceed 40 mol %, preferably 20 mol % and more preferably 10mol % based on the sum of ethylene oxide and propylene oxide unitspolymerized in the block. They are preferably pure polyethylene oxideblocks. The hydrophobic blocks may, for example, be blocks ofpolypropylene oxide or C₄- to C₁₂-alkylene oxides. In addition,hydrophobic blocks can be formed, for example, from hydrocarbon units or(meth)acrylic esters.

Preferred polymeric cosurfactants (M3) comprise polypropyleneoxide-polyethylene oxide block copolymers, polyisobutene-polyethyleneoxide block copolymers, and comb polymers with polyethylene oxide sidechains and a hydrophobic main chain, where the main chain preferablycomprises essentially olefins or (meth)acrylates as components. The term“polyethylene oxide” here shall in each case include polyethylene oxideblocks as defined above comprising propylene oxide units. Furtherdetails of the preferred polymeric cosurfactants (M3) are disclosed inWO 2006/131541.

The examples which follow illustrate the invention:

I) Preparation of the Starting Materials

EXAMPLE A Preparation of an Aliphatic, Branched C₁₇ Alcohol R¹—OH with aDegree of Branching of 3.1

Olefin Oligomerization:

In an isothermal reactor of length about 1.5 m and of diameter 30 mm,Raffinate II of the following compositions was converted over aheterogeneous catalyst at 20 bar and 80° C.

i-butane: 3% by weight

n-butane: 15% by weight

i-butene: 2% by weight

butene-1: 30% by weight

butene-2-trans: 32% by weight

butene-2-cis: 18% by weight

The catalyst used was a material which had been prepared according toDE-A-43 39 713 in the form of tablets (5 mm×5 mm). The composition in %by weight of the active components was: 50% by weight of NiO, 12.5% byweight of TiO₂, 33.5% by weight of SiO₂, 4% by weight of Al₂O₃. Thethroughput was 0.75 kg of Raffinate II/(I (cat)×h). There was norecycling of C₄ hydrocarbons. The C₄ conversion based on the butenespresent in the Raffinate 11 was 52.0% by weight.

The selectivity in % by weight was as follows: C₈: 76.9; C₁₂: 18.4 andC₁₆₊: 4.7.

Distillation of the C₁₆₊ Mixture:

The crude C₁₆₊ mixture was distilled in an industrial distillation plantconsisting of two columns with packing height approx. 15 m in each case(250 m²/m³). In the first column (forerun column), low boilers stillpresent (in particular C₁₂-olefins) were removed overhead. In the secondcolumn (main run column), the C₁₆-olefin was removed with a purityof >99% overhead, while the C₂₀₊ olefins were removed in the bottom.

The two columns were operated with the following parameters:

Forerun column Main run column Top temperature 135° C. 165° C. Bottomtemperature 180-182° C. 225-230° C. Pressure (top) 85 mbar 60 mbarPressure drop over packing approx. 5 mbar approx. 50 mbar Feed 2700 kg/h2500 kg/h Top draw 200 kg/h 1700 kg/h Reflux 850 kg/h 3000 kg/h Bottoms2500 kg/h 800 kg/hHydroformylation:

The hydroformylation plant described in EP 1204624 was chargedcontinuously with 2.2 t/h of C₁₆-olefin and 0.2 t/h of an aqueous cobaltsalt solution. The following conditions were established in the reactor:

Cobalt concentration 0.10% by weight

Temperature 185° C.

Pressure (CO/H₂ approx. 1:1) 280 bar

The effluent of the hydroformylation was, as described in EP 1204624,freed of cobalt by oxidation, and then hydrogenated in the hydrogenationplant described in DE 10036172 over the Co/Cu/Mo catalyst describedthere to the alcohol. The following parameters were established:

Temperature 160° C.

Pressure (H₂) 280 bar

The crude alcohol thus obtained was purified in the above-describeddistillation plant under the following conditions to give the purealcohol.

Forerun column Main run column Top temperature 155° C. 214° C. Bottomtemperature 222° C. 235° C. Pressure (top) 60 mbar 60 mbar Pressure dropover packing 20 mbar 20 mbar Feed 2450 kg/h 2000 kg/h Top draw 450 kg/h1800 kg/h Reflux 850 kg/h 900 kg/h Bottoms 2000 kg/h 200 kg/h

Method for determining the iso index of the C₁₇ alcohol mixture by meansof ¹H NMR: Approx. 20 mg of C₁₇ alcohol mixture are dissolved in 0.4 mlof CDCl₃ and a small amount of TMS is added for frequency referencing.Thereafter, the solution is admixed with 0.2 ml of TAI, transferred to a5 mm NMR tube and analyzed in an NMR spectrometer.

Analysis Conditions:

-   -   Spectrometer frequency: 400 MHz    -   Relaxation delay: 10 s    -   Pulse angle: 30°    -   Data points recorded: 64 K    -   Number of scans: 64    -   Transformed data points: 64 K    -   Exponential multiplication: 0.2 Hz

Fourier transformation and automatic phase and base line correction werefollowed by manual integration of the 4.7 to 3.7 ppm (all primaryalcohols esterified with TAI) and 2.4 to −0.4 ppm (all methyl, methyleneand methine protons) ranges. The zero order integral phases are selectedsuch that the start and end of the integral curves run essentiallyhorizontally. The signals <1 ppm are assigned to the methyl groups.

The iso index thus determined is: 3.1

II) Preparation of Surfactants

EXAMPLE 1 Preparation of a Nonionic Surfactant (iC₁₇ Alcohol+10 EthyleneOxide by KOH Catalysis)

The branched C₁₇H₃₅ alcohol according to example A (250.4 g, 1.019 mol)is admixed with KOH solution (50%, 4.2 g, 0.037 mol) in a 2 l pressureautoclave from Mettler, and dewatered at 100° C. and 15 mbar for 3 h.Subsequently, the mixture is inertized twice with nitrogen (up to 5bar), an upstream pressure of 1 bar is established and the mixture isheated to 130° C. Within 4.5 h, ethylene oxide (449 g, 10.19 mol) ismetered in up to a maximum pressure of 7 bar and the mixture is stirredafter the addition has ended for another 3 h.

Finally, the compound is degassed under reduced pressure (15 mbar),admixed with Ambosol (3 percent by weight) and filtered.

iC₁₇-10 EO is obtained (weight 700 g, theory 707 g; OH number 78.2 mgKOH/g, theory 81.8 mg KOH/g) as a clear liquid.

The molar mass distribution of the surfactant was determined by means ofsize exclusion chromatography.

EXAMPLE 2 Preparation of a Nonionic Surfactant (iC₁₇ Alcohol+10 EthyleneOxide by DMC Catalysis)

The branched C₁₇H₃₅ alcohol according to example A (308.4 g, 1.255 mol)is mixed with DMC catalyst (Zn—Co cyanide complex, 0.86 g) byUltraturax, transferred to a 2 l pressure autoclave from Mettler, anddewatered at 110° C. and <10 mbar for 2 h. Subsequently, the mixture isinertized twice with nitrogen (up to 5 bar), an upstream pressure of 1bar is established and the mixture is heated to 130° C. Ethylene oxide(552 g, 12.55 mol) is metered in up to a maximum pressure of 7 barwithin 5.2 h and the mixture is stirred for another 4 h after theaddition has ended.

Finally, the product is degassed under reduced pressure (15 mbar) andfiltered. iC₁₇-10 EO is obtained (weight 857 g, theory 861 g; OH number81.1 mg KOH/g, theory 81.8 mg KOH/g) as a clear liquid.

The molar mass distribution of the surfactant was determined by means ofsize exclusion chromatography. The surfactant prepared by DMC catalysishad a significantly narrower molar mass distribution than the surfactantprepared by KOH catalysis according to example 3.

EXAMPLE 3 Preparation of a Nonionic Surfactant (iC₁₇ Alcohol+2 EthyleneOxide by DMC Catalysis)

The branched C₁₇H₃₅ alcohol according to example A (477.7 g, 1.944 mol)is mixed with DMC catalyst (Zn—Co cyanide complex, 0.65 g) byUltraturax, transferred to a 2 l pressure autoclave from Mettler anddewatered at 110° C. and <10 mbar for 2 h. Subsequently, the mixture isinertized twice with nitrogen (up to 5 bar), an upstream pressure of 1bar is established and the mixture is heated to 130° C. Ethylene oxide(171.1 g, 3.888 mol) is metered in up to a maximum pressure of 7 barwithin 1.2 h and the mixture is stirred for a further 10 h after theaddition has ended.

Finally, the product is degassed under reduced pressure (15 mbar) andfiltered. iC₁₇-2 EO is obtained (weight 641 g, theory 649 g; OH number171 mg KOH/g, theory 168.1 mg KOH/g) as a clear liquid.

EXAMPLE 4 Preparation of an Ionic Surfactant (iC₁₇ Alcohol-2 EO-SO₃H)

1st Stage

iC₁₇-2 EO (98 g, 0.3 mol) from example 1 is cooled to 10° C. in a 500 mlmultineck flask with precision glass stirrer, reflux condenser, gasinlet tube and temperature sensor, and admixed dropwise at thistemperature with thionyl chloride (39.2 g, 0.33 mol). After stirring at20° C. for 1 h, an N₂ stream is passed through the solution which isheated slowly to 60° C. Subsequently, the mixture is stirred at 110° C.for 3 h. A titrimetric determination of the chloride ion content (withAgNO₃) showed complete conversion and removal of HCl. The structureiC₁₇-2 EO—Cl was confirmed spectroscopically (IR, 1H NMR).

2nd Stage

iC₁₇-2 EO—Cl (52.82 g, 0.15 mol) is mixed in a 300 ml autoclave withiPrOH (25 g), sodium sulfite (20.8 g, 0.165 mol), distilled water (78 g)and sodium hydroxide solution (50%, 0.75 g). After purging with N₂, themixture is heated to 160° C. at 500 revolutions per minute, stirred atthis temperature for 30 h and cooled again to room temperature. Atitrimetric determination of the chloride ion content (with AgNO₃)showed complete conversion. Subsequently, the mixture is freed from thesolvent. iC₁₇-2 EO—SO₃H is obtained.

COMPARATIVE EXAMPLE 1 Nonionic Surfactant Based on an Arylalkyl Alcohol(Dodecylphenol+10 EO by KOH Catalysis)

4-Dodecylphenol (209.4 g, 0.798 mol; Aldrich) is admixed with KOHsolution (50%, 3.36 g, 0.03 mol) in a 2 l pressure autoclave fromLabmax, and dewatered at 100° C. and 15 mbar for 2 h. Subsequently, themixture is inertized twice with nitrogen (up to 5 bar), an upstreampressure of 1 bar is established and the mixture is heated to 130° C.Ethylene oxide (351 g, 7.98 mol) is metered in up to a maximum pressureof 7 bar within 3 h, and the mixture is stirred for another 5 h afterthe addition has ended. Finally, the compound is degassed under reducedpressure (15 mbar), admixed with Ambosol (3 percent by weight) andfiltered. Dodecylphenol—10 EO is obtained (weight 560 g, theory 561.6 g;OH number 82.8 mg KOH/g, theory 79.9 mg KOH/g) as a clear liquid.

COMPARATIVE EXAMPLE 2 Nonionic Surfactant Based on an Arylalkyl Alcohol(Dodecylphenol+13 EO by KOH Catalysis)

The procedure of comparative example 1 was repeated, except that adegree of ethoxylation of 13 was established.

COMPARATIVE EXAMPLE 3 Nonionic Surfactant Based on a Linear Alcohol(C₁₆-C₁₈ Fatty Alcohol+10 EO by KOH Catalysis)

C₁₆-C₁₈ fatty alcohol (403 g, 1.586 mol) is admixed with KOH solution(50%, 6.6 g, 0.057 mol) in a 2 l pressure autoclave and dewatered at 95°C. and 15 mbar for 2 h. Subsequently, inertization is effected twicewith nitrogen (up to 5 bar), a preliminary pressure of 1 bar isestablished and the mixture is heated to 130° C. Within 3 h, ethyleneoxide (698 g, 15.86 mol) is metered in up to a maximum pressure of 8 barand, after addition has ended, the mixture is stirred for a further 5 h.

Finally, the compound is degassed under reduced pressure (15 mbar),admixed with Ambosol (3% by weight) and filtered. This affords C₁₆C₁₈fatty alcohol 10 EO (weight 1080 g, theory 1108 g; OH number 89.2 mgKOH/g, theory 80.8 mg KOH/g) as a solid.

COMPARATIVE EXAMPLE 4 Nonionic Surfactant Based on2-methylhexadecan-1-ol (2-methylhexadecan-1-ol+10 EO by KOH Catalysis)

1st Stage

A 1 molar solution of lithium diisopropylamide (300 ml, 300 mmol) intetrahydrofuran was added dropwise at −78° C. under a nitrogenatmosphere to a solution of methyl palmitate (32.4 g, 120 mmol) in drytetrahydrofuran (1500 ml). After adding DMPU (57.2 g, 447 mmol), thesolution was warmed to −20° C. and stirred at this temperature for 1 h.After cooling again to −78° C., methyl iodide (306 g, 2150 mmol) wasadded dropwise and the mixture was warmed to 20° C. After addingsaturated NH4Cl solution (1000 ml) and phase separation, the mixture wasextracted with ethyl acetate (3×1000 ml), and the combined organicphases were dried over sodium sulfate and freed of the solvent underreduced pressure. The crude mixture was purified by columnchromatography on silica gel. This afforded the methylated methylpalmitate in a 94% yield (32 g).

2nd Stage

The end product from stage 1 (210 g, 740 mmol) was added at 20° C. to asolution of lithium aluminum hydride (84 g, 2210 mmol) intetrahydrofuran (3500 ml), and the mixture was stirred at thistemperature for 24 h. The mixture was heated to reflux until no signalof a carbonyl group was observable any longer in the IR. After coolingto 20° C., Na2SO4 was added until no further hydrogen formed. Afterfiltration, the mixture was freed of the solvent under reduced pressureand the alcohol was obtained in a yield of 92.5% (175 g). Analysis bygas chromatography and ¹H NMR spectroscopy showed that the resultingalcohol consists to an extent of 87% of 2-methylhexadecan-1-ol, 11%2,2-dimethylhexadecan-1-ol and 2% hexadecan-1-ol.

3rd Stage

2-Methylhexadecan-1-ol (40 g, 0.156 mol) is admixed with KOH solution(50%, 0.6 g, 0.006 mol) in a 300 ml pressure autoclave and dewatered at100° C. and 15 mbar for 2 h. Subsequently, the mixture is inertizedthree times with nitrogen (up to 3 bar), a preliminary pressure of 1 baris established and the mixture is heated to 130° C. Within 50 min,ethylene oxide (68.6 g, 1.56 mol) is metered in up to a maximum pressureof 8 bar and, after the addition has ended, stirring is continued foranother 5 h.

Finally, the compound is degassed under reduced pressure (15 mbar),admixed with Ambosol (3% by weight) and filtered. This affords2-methylhexadecan-1-ol 10 EO (weight 102 g, theory 109 g). The structurewas confirmed by ¹H NMR spectroscopy and size exclusion chromatography(SEC).

III) Performance Tests

The surfactants obtained were used to carry out the following tests inorder to assess their suitability for tertiary mineral oil extraction.

Description of the Test Methods

Determination of SP*

a) Principle of the Measurement:

The interfacial tension between water and oil was determined in a knownmanner by means of the measurement of the solubilization parameter SP*.The determination of the interfacial tension by means of thedetermination of the solubilization parameter SP* is a method widelyaccepted in the technical field for approximate determination of theinterfacial tension. The solubilization parameter SP* reports how manyml of oil are dissolved in a microemulsion (Windsor type III) per ml ofsurfactant used. The interfacial tension σ (IFT) can be calculatedtherefrom via the approximation formula IFT≈0.3/(SP*)² if the samevolumes of water and oil are used (C. Huh, J. Coll. Interf. Sc., Vol.71, No. 2 (1979)).

b) Method

To determine the SP*, a 100 ml measuring cylinder with a magneticstirrer bar is charged with 20 ml of oil and 20 ml of water. To this areadded 5% by weight or 2.5% by weight of surfactant (the latter if anSP*>10 is to be determined). Subsequently, the temperature is increasedstepwise from 20 to 90° C., and the temperature window in which amicroemulsion formed is observed.

The formation of the microemulsion can be observed visually or else withthe aid of conductivity measurements. A triphasic system forms (upperphase oil, middle phase microemulsion, lower phase water). When upperand lower phase are of equal size and do not change any further over aperiod of 12 h, the optimal temperature (T_(opt)) of the microemulsionhas been found. The volume of the middle phase is determined. The volumeof surfactant added is subtracted from this volume. The value obtainedis then divided by two. This volume is then divided by the volume ofsurfactant added. The result is noted as SP*.

The type of oil and water used to determine SP* is determined accordingto the system to be studied. Firstly, it is possible to use mineral oilitself, or else a model oil, for example decane or hexadecane. The waterused may either be pure water or saline water, in order to better modelthe conditions in the mineral oil formation. The composition of theaqueous phase can, for example, be adjusted according to the compositionof a particular deposit water.

Information regarding the aqueous phase used and the oil phase can befound below in the specific description of the tests.

Test Results

Determination of the Solubility of the Surfactants

For the solubility tests, high-salinity water was used (salt content inpercent by weight: 13.2% NaCl, 4.26% CaCl₂, 1.05% MgCl₂, 0.03% Na₂SO₄),which is typical for a mineral oil deposit in northern Germany.

The salt solution was admixed in each case with 1% by weight ofsurfactant, and the appearance of the solution at various temperatureswas assessed. The results are compiled in table 1. The solubilitybehavior of the surfactants from example 1 and from comparative example1 is relatively similar.

Determination of the Interfacial Tension (IFT)

The interfacial tension was determined in each case by the generalmethod described above.

The oil used was decane and the aqueous phase used was the salt wateralso used in the solubility tests (salt content in percent by weight:13.2% NaCl, 4.26% CaCl₂, 1.05% MgCl₂, 0.03% Na₂SO₄). The results aresummarized in table 2. ΔT indicates the temperature window within whichthe microemulsion occurs, and T_(opt) the optimal temperature asdetermined above.

In addition, tests were carried out with crude oils. Two differentmedium heavy crude oils of different origin and viscosity were used. Theaqueous phase used was in each case a salt solution whose compositioncorresponded to the deposit water of the crude oil used. Details aresummarized in table 3. The test temperature used in each case was theappropriate deposit temperature. The interfacial tensions measured areeach summarized in table 4.

The results show that the inventive surfactants with highly branchedaliphatic radicals achieve lower interfacial tensions in the water-oilsystem than other surfactants.

Comparison of Interface Tension and Phase Separation Time and Solubilityas a Function of the Degree of Branching in the Hydrophobic Part ofSurfactants

The interface tension was in each case determined by the general methoddescribed above.

The oil used was hexadecane, and the aqueous phase used the salt wateralso used in the solubility tests (salt content in percent by weight:13.2% NaCl, 4.26% CaCl₂, 1.05% MgCl₂, 0.03% Na₂SO₄). The water:oil ratiois 1:1(20 ml:20 ml). The surfactant concentration is 2.5% by volume inrelation to the combined volume of oil and water.

The results are compiled in Table 5. T_(opt) indicates the optimaltemperature determined as above. In the last column is the time for theformation of the balanced middle phase (microemulsion). This phaseseparation time t is minimal if a balanced microemulsion is present,which means that equal volumes of oil and water are present in additionto the middle phase.

A rapid phase separation time is desired, in order that the oil bank candevelop very rapidly in the formation. In the case of crude oils, thephase separation is significantly slower than in the case ofcorresponding model oils composed of n-alkanes (according to expedience,a factor of 50). The literature discloses additions of short-chainalcohols, which, however, significantly influence the optimaltemperature and the interface tension.

The solubility was assessed visually using 2.5% surfactant in theNorthern German water described (salt content in percent by weight:13.2% NaCl, 4.26% CaCl₂, 1.05% MgCl₂, 0.03% Na₂SO₄) at differenttemperatures. The results are compiled in Table 6.

The results show that numerous advantages can be achieved with theinventive surfactants with highly branched aliphatic radicals comparedto surfactants with lower degrees of branching:

Lower interface tensions are obtained than in the case ofalkylphenyl-based surfactants with a similar hydrophobic-hydrophilicbalance (recognizable by similar T_(opt)) (see Tables 2 and 4).

Exceptionally small phase separation times. As can be seen from Table 5,the phase separation time for the inventive surfactant at T_(opt) isonly 2 min, whereas the linear surfactant according to comparativeexample 3 and the surfactant with a degree of branching of only 1according to comparative example 4 each have phase separation times of80 min.

Reduction in the phase separation times while maintaining the lowinterface tension with addition of inventive surfactants to surfactantswhich have a low interface tension but high phase separation times.Synergistic action as can be seen in Table 5.

The inventive surfactants have better solubilities in thesurfactant-water system, especially at relatively low temperatures, ascan be seen in Tables 1 and 6.

TABLE 1 Results of the solubility test No. Surfactant RT 60° C. 90° C.Comparative Dodecylphenol - Turbid Turbid Turbid example 1 10 EO withoutwithout without sediment sediment sediment Example 1 iC₁₇ - 10 EO ClearTurbid Small without flocs sediment

TABLE 2 Interfacial tension in the water-decane system for varioussurfactants IFT [mN/m] T_(opt) ΔT No. Surfactant SP* at T_(opt) [° C.][° C.] Comparative Dodecylphenol - 2.8 0.038 52.5 5 example 1 10 EO (KOHcatalysis) Comparative Dodecylphenol - 1.1 0.248 69 16 example 2 13 EO(KOH catalysis) Example 1 iC₁₇ - 10 EO 8 0.005 66.6 2 (KOH catalysis)Example 2 iC₁₇ - 10 EO 11.5 0.002 63.2 1.5 (DMC catalysis)

TABLE 3 Oils and aqueous phases used for the tests Density at Salts inExtraction Deposit 23° C. the aqueous site temperature Viscosity [g/cm³]phase Crude Northern 54° C. 66 mPas (20° C.) 0.885 13.2% NaCl, 4.26%CaCl₂, 1.05% MgCl₂, oil A Germany 17 mPas (50° C.) 0.03% Na₂SO₄ CrudeOman 69° C. 25 mPas (20° C.) 0.873 16.5% NaCl, 6.08% CaCl₂ * 2 H₂O, 1.9%oil B  8 mPas (50° C.) MgCl₂ * 6 H₂O, 0.03% Na₂SO₄

TABLE 4 Results of the measurements of the interfacial tensionSurfactant used Crude oil No. Name SP* IFT [mN/m] Crude oil AComparative Dodecylphenol - 2 0.075 example 1 10 EO Crude oil A Example1 iC₁₇ - 10 EO 3 0.033 Crude oil B Comparative Dodecylphenol - not notexample 1 10 EO determin- determin- able able Crude oil B Example 1iC₁₇ - 10 EO 19 0.0008

TABLE 5 Interface tension and phase separation in the Northern Germanwater - hexadecane system for different surfactants IFT Surfactant used[mN/m] T_(opt) t [min] No. Designation Degree of branching SP* atT_(opt) [° C.] at T_(opt) Comparative example 3 C16C18 fatty alcohol -10 EO 0 8 0.005 59.4 80 (KOH catalysis) Comparative example 42-methylhexadecanol - 10 EO approx. 1 7.25 0.005 58 80 (KOH catalysis)Example 1 iC₁₇ - 10 EO approx. 3.1 3 0.033 62.3 2 (KOH catalysis) 30:70Mixture of iC₁₇ - 10 EO (KOH catalysis): (0.3 × approx. 3.1) + 6 0.00860.1 5 example 1 and C16C18 fatty alcohol - 10 EO (0.7 × 0) = approx. 1comparative example 3 (KOH catalysis) ratio 30:70 50:50 Mixture of 2.5%C₁₆-C₁₈ fatty alcohol - 10 EO + 0 2.5 0.048 46.8 10 comparative example3 2.5% nC4 - 1 EO and butyl monoglycol

TABLE 6 Results of the solubility tests No. Surfactant RT 50° C.Comparative C16C18 fatty alcohol - flocculated turbid example 3 10 EO(KOH catalysis) without sediment Example 1 iC₁₇ - 10 EO clear turbidwithout sediment Comparative 2-methylhexadecanol - turbid turbid example4 10 EO (KOH catalysis) without without sediment sediment 30:70 MixtureiC₁₇ - 10 EO (KOH slightly slightly of example 1 catalysis): C16C18turbid turbid and fatty alcohol - without without comparative 10 EO (KOHcatalysis) sediment sediment example 3 ratio 30:70

The invention claimed is:
 1. A method of tertiary mineral oil extractionfrom a mineral oil deposit, the method comprising: injecting asurfactant of the general formula R¹—X, where R¹ is an aliphaticC₁₇H₃₅-alkyl radical and X is a hydrophilic group selected from thegroup consisting of sulfonate groups, polyoxyalkylene groups,anionically modified polyoxyalkylene groups, glucoside groups, amineoxide groups, cationic groups, and betainic groups, wherein the meandegree of branching of the R¹ radical is from 2.8 to 3.7, in the form ofan aqueous formulation into the mineral oil deposit through an injectionbore, and withdrawing crude oil from the deposit through a productionbore.
 2. The method according to claim 1, wherein the mean degree ofbranching of the R¹ radical is from 3.01 to 3.5.
 3. The method accordingto claim 1, which comprises alkyl alkoxylates (A) which comprise alkoxyand/or ethoxy groups and are of the general formulaR¹O—(CH₂CH(R²)O)_(n)(CH₂CH₂O)_(m)—H  (I) where R² is a straight-chain,branched, aliphatic or aromatic hydrocarbon radical having from 1 to 10carbon atoms, n is from 0 to 15, m is from 1 to 20, and k=n+m for valuesfrom 1 to 35, with the proviso that the alkoxy and ethoxy groups—whereboth types of groups are present—may be arranged randomly, alternatelyor in block structure.
 4. The method according to claim 3, wherein m isgreater than n.
 5. The method according to claim 3, wherein R² is amethyl group.
 6. The method according to claim 3, wherein, in formula(I), n≧1 and the surfactant is a block copolymer in which the alkoxy andethoxy groups are arranged in the sequence specified in formula (I). 7.The method according to claim 3, wherein m is from 5 to
 14. 8. Themethod according to claim 1, which comprises alkyl ether sulfonates (B)which comprise alkoxy and/or ethoxy groups and are of the generalformulaR¹O—(CH₂CH(R²)O)_(n′)(CH₂CH₂O)_(m′)—R³—SO₃M  (II) where R² is astraight-chain, branched, aliphatic or aromatic hydrocarbon radicalhaving from 1 to 10 carbon atoms, n′ is from 0 to 15, m′ is from 1 to20, k′=n′+m′ is from 1 to 35, M is H⁺ and/or a k-valent counterion 1/xY^(x+), and R³ is a divalent hydrocarbon group which has from 2 to 12carbon atoms and may optionally have functional groups as substituents,with the proviso that the alkoxy and ethoxy groups—where both types ofgroups are present—may be arranged randomly, alternately or in blockstructure.
 9. The method according to claim 1, which comprises alkylether carboxylates (C) which comprise alkoxy and/or ethoxy groups andare of the general formulaR¹O—(CH₂CH(R²)O)_(n″)(CH₂CH₂O)_(m″)—R⁵—COOM  (III) where R² is astraight-chain, branched, aliphatic or aromatic hydrocarbon radicalhaving from 1 to 10 carbon atoms, n″ is from 0 to 15, m″ is from 1 to20, k″=n″+m″ is from 1 to 35, M is H⁺ and/or a k-valent counterion 1/xY^(x+), and R⁵ is a divalent hydrocarbon group having from 1 to 12carbon atoms, with the proviso that the alkoxy and ethoxy groups—whereboth types of groups are present—may be arranged randomly, alternatelyor in block structure.
 10. The method according to claim 1, whichcomprises alkyl ether sulfates (D) which comprise alkoxy and/or ethoxygroups and are of the general formulaR¹O—(CH₂CH(R²)O)_(n′″)(CH₂CH₂O)_(m′″)—SO₃M  (IV) where R² is astraight-chain, branched, aliphatic or aromatic hydrocarbon radicalhaving from 1 to 10 carbon atoms, n′″ is from 0 to 15, m′″ is from 1 to20, k′″=n′″+m′″ is from 1 to 35, and M is H⁺ and/or a k-valentcounterion 1/x Y^(x+), with the proviso that the alkoxy and ethoxygroups—where both types of groups are present—may be arranged randomly,alternately or in block structure.
 11. The method according to claim 8,wherein m′ is greater than n′.
 12. The method according to claim 8,wherein R² is a methyl group.
 13. The method according to claim 8,wherein, in the formula (II) n′ is ≧1 and the surfactant is a blockcopolymer in which the alkoxy and the ethoxy groups and the sulfonicacid group or the carboxyl group or the sulfate group are arranged inthe sequence specified in formula (II).
 14. The method according toclaim 8, wherein m′ is from 1 to
 15. 15. The method according to claim1, which comprises alkylpolyglucosides (E) of the general formula

where 1 is from 0 to
 2. 16. The method according to claim 1, whichcomprises amine oxides of the general formula

where R⁶ and R⁷ are each independently methyl or hydroxyethyl radicals.17. The method according to claim 9, wherein m″ is greater than n″. 18.The method according to claim 10, wherein m″′ is greater than n″′. 19.The method according to claim 9, wherein, in the formula (III) n″ is ≧1and the surfactant is a block copolymer in which the alkoxy and theethoxy groups and the sulfonic acid group or the carboxyl group or thesulfate group are arranged in the sequence specified in the formula(III).
 20. The method according to claim 10, wherein, in the formula(IV) n′″ is ≧1 and the surfactant is a block copolymer in which thealkoxy and the ethoxy groups and the sulfonic acid group or the carboxylgroup or the sulfate group are arranged in the sequence specified in theformula (IV).
 21. The method according to claim 9, wherein m″ is from 1to
 15. 22. The method according to claim 10, wherein m″′ is from 1 to15.
 23. A method of tertiary mineral oil extraction from a mineral oildeposit, the method comprising: injecting an aqueous formulation of asurfactant mixture (M) comprising at least two different surfactants,wherein at least one surfactant is a surfactant of the general formulaR¹—X, where R¹ is an aliphatic C₁₇H₃₅-alkyl radical and X is ahydrophilic group, and wherein the mean degree of branching of the R¹radical is from 2.8 to 3.7, into the mineral oil deposit through aninjection bore, and withdrawing crude oil from the mineral oil depositthrough a production bore, wherein the surfactant mixture (M) comprisesat least one nonionic surfactant (M1) and at least one anionicsurfactant (M2).
 24. The method according to claim 23, which comprisesat least one surfactant (M1′) with nonionic behavior and at least onesurfactant (M2′) with ionic behavior.
 25. The method according to claim23, wherein the surfactant mixture (M) comprises at least one alkylalkoxylate (A) which comprises alkoxy and/or ethoxy groups and is of thegeneral formulaR¹O—(CH₂CH(R²)O)_(n)(CH₂CH₂O)_(m)—H  (I) where R² is a straight-chain,branched, aliphatic or aromatic hydrocarbon radical having from 1 to 10carbon atoms, n is from 0 to 15, m is from 1 to 20, and k=n+m for valuesfrom 1 to 35, with the proviso that the alkoxy and ethoxy groups—whereboth types of groups are present—may be arranged randomly, alternatelyor in block structure, and/or an alkyl ether sulfonate (B) whichcomprises alkoxy and/or ethoxy groups and is of the general formulaR¹O—(CH₂CH(R²)O)_(n′)(CH₂CH₂O)_(m′)—R³—SO₃M  (II) where R² is astraight-chain, branched, aliphatic or aromatic hydrocarbon radicalhaving from 1 to 10 carbon atoms, n′ is from 0 to 15, m′ is from 1 to20, k′=n′+m′ is from 1 to 35, M is H⁺ and/or a k-valent counterion 1/xY^(x+), and R³ is a divalent hydrocarbon group which has from 2 to 12carbon atoms and may optionally have functional groups as substituents,with the proviso that the alkoxy and ethoxy groups—where both types ofgroups are present—may be arranged randomly, alternately or in blockstructure.
 26. The method according to claim 23, wherein the surfactantmixture (M) comprises at least one surfactant R⁸—X where R⁸ is analiphatic or araliphatic C₁₆-C₂₀ hydrocarbon radical and X is thehydrophilic group.
 27. The method according to claim 26, wherein thesurfactant R⁸—X is an alkyl alkoxylate of the general formulaR⁸—(CH₂CH(R²)O)_(n)(CH₂CH₂O)_(m)—H  (VII) or an alkyl ether sulfonate ofthe general formulaR⁸O—(CH₂CH(R²)O)_(n′)(CH₂CH₂O)_(m′)—R³—SO₃M  (VIII) where R² is astraight-chain, branched, aliphatic or aromatic hydrocarbon radicalhaving from 1 to 10 carbon atoms, n is from 0 to 15, m is from 1 to 20,k=n+m for values from 1 to 35, n′ is from 0 to 15, m′ is from 1 to 20,k′=n′+m′ is from 1 to 35, M is H⁺ and/or a k-valent counterion 1/xY^(x+), and R³ is a divalent hydrocarbon group which has from 2 to 12carbon atoms and may optionally have functional groups as substituents,with the proviso that the alkoxy and ethoxy groups—where both types ofgroups are present—may be arranged randomly, alternately or in blockstructure.
 28. The method according to claim 23, wherein the surfactantmixture (M) additionally comprises up to 49.9% by weight, based on thesum of all surfactants in the mixture, of at least one polymericcosurfactant (M3).
 29. The method according to claim 28, wherein thepolymeric cosurfactant (M3) is a block copolymer which comprises atleast one hydrophobic block and at least one hydrophilic block.
 30. Themethod according to claim 28, wherein the polymeric cosurfactant (M3) isa polymer selected from the group of polypropylene oxide-polyethyleneoxide block copolymers, polyisobutene-polyethylene oxide blockcopolymers, and comb polymers with polyethylene oxide side chains and ahydrophobic main chain.
 31. The method according to claim 23, whereinthe surfactant mixture (M) further comprises a solvent or a solventmixture.